5. Installation. A good window without a good installation won't last, so consider this: Whatever type of siding you have — wood, vinyl, even brick — water will get behind the siding and run down the wall sheathing behind it. So think about the path that water will take when it gets to you window. Building wrap, like Tyvek, should be lapped over so water can't run behind the window. Flashing tape should be used to seal the window's installation flanges to the sheathing. If you are remodeling, install metal head flashing to divert water around the window and pay special attention to caulking.